[PATCH v3 2/2] of: reserved_mem: allocate and map the reserved_mem array early

[Geert Uytterhoeven]

Hi Marek,

On Thu, 15 Oct 2026 at 10:29, Marek Szyprowski <m.szyprowski at samsung.com> wrote:
> Get rid of the static, limited-size reserved_mem array and replace it
> with array allocated by memblock_alloc_raw() and accessed directly or
> through a temporary early_memremap() mapping (depending on the
> architecture support). Such mapping is needed for some architectures
> (like ARM64), where linear map is not yet available during early boot
> scan. The array is allocated from the bottom of RAM to avoid placing it
> in highmem area, because some architectures (e.g. Xtensa, C-SKY, MIPS32)
> set the memblock limit to the end of lowmem only after the early scan.
> The early mapping is not used on PPC64, where the scan is done before
> early_ioremap_setup(), but the memory allocated by memblock is already
> accessible at that point.
>
> Having a single, writeable array with all reserved regions removes the
> need to perform two step initialization introduced by commit
> 8a6e02d0c00e ("of: reserved_mem: Restructure how the reserved memory
> regions are processed"), so all regions can be processed during the
> early scan again.
>
> The reserved_mem array is allocated only after all static (defined by
> the 'reg' property) regions are marked as reserved or no-map, so it
> cannot be placed in any of them. Errors of the early reservations are
> not recorded per region, only the fact that some of them failed is
> stored and a message asking to fix the device-tree is printed. The
> region specific init functions for the static regions are then called
> in a separate pass, once the array is available. Then all dynamically
> allocated reserved regions are processed.
>
> Suggested-by: Mike Rapoport <rppt at kernel.org>
> Link: https://lore.kernel.org/all/asc6brs_g0ky0wOM@kernel.org/
> Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>

Thanks for your patch, which is now commit aa05faf815836c47 ("of:
reserved_mem: allocate and map the reserved_mem array early")
in dt-rh/for-next.

This causes an early crash on BeagleV Starlight Beta:

 [...]
 earlycon: uart0 MMIO32:0x0000000012440000 (options '115200n8')
 printk: legacy bootconsole [uart0] enabled
 printk: debug: skip boot console de-registration.
 efi: UEFI not found.
-OF: reserved mem: 0x00000000fb000000..0x00000000fcffffff (32768 KiB)
map non-reusable framebuffer at fb000000
-OF: reserved mem: 0x00000000f9000000..0x00000000f9ffffff (16384 KiB)
map non-reusable framebuffer at f9000000
-OF: reserved mem: 0x00000000d0000000..0x00000000f7ffffff (655360 KiB)
map non-reusable framebuffer at d0000000
-OF: reserved mem: 0x00000000c9000000..0x00000000ccffffff (65536 KiB)
map non-reusable framebuffer at c9000000
-OF: reserved mem: 0x00000000fa000000..0x00000000faffffff (16384 KiB)
nomap non-reusable dma-reserved at fa000000
-Reserved memory: created DMA memory pool at 0x000000107a000000, size 16384 KiB
-OF: reserved mem: initialized node linux,dma at 107a000000, compatible
id shared-dma-pool
-OF: reserved mem: 0x000000107a000000..0x000000107affffff (16384 KiB)
nomap non-reusable linux,dma at 107a000000
-SBI HSM extension detected
-[...]
+Oops - store (or AMO) access fault [#1]
+Modules linked in:
+CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted
7.4.0-rc1-starlight-00002-gaa05faf81583 #411 PREEMPT
+Hardware name: BeagleV Starlight Beta (DT)
+epc : __memset+0x68/0xfe
+ ra : fdt_scan_reserved_mem+0x3a4/0x80a
+epc : ffffffff8087fd88 ra : ffffffff80a313c8 sp : ffffffff81403c20
+ gp : ffffffff814dc6c0 tp : ffffffff8140cf80 t0 : ffffffc4fea38ff0
+ t1 : 0000000080200000 t2 : ffffffc4fec03008 s0 : ffffffff81403d10
+ s1 : ffffffffffffffff a0 : ffffffc4fea39000 a1 : 0000000000000000
+ a2 : 00000000000000f0 a3 : ffffffc4fea390f0 a4 : 0000000000000008
+ a5 : ffffffff8087fd88 a6 : 00000000000000f0 a7 : 0000000000001000
+ s2 : ffffffc4fec00000 s3 : 00000000000000f0 s4 : 0000000000000000
+ s5 : 0000000000002de0 s6 : 0000000000000006 s7 : fffffffffefefefe
+ s8 : ffffffc4fec02fd4 s9 : ffffffff8148e318 s10: fffffffffefefeff
+ s11: ffffffc4fea39000 t3 : ffffffff8150df00 t4 : ffffffff8150df00
+ t5 : ffffffff8150df00 t6 : ffffffff8150df78 ssp : 0000000000000000
+status: 0000000200000100 badaddr: ffffffc4fea39000 cause: 0000000000000007
+[<ffffffff8087fd88>] __memset+0x68/0xfe
+[<ffffffff80a2f63a>] early_init_fdt_scan_reserved_mem+0xa4/0x110
+[<ffffffff80a06c8e>] paging_init+0x17c/0x46a
+[<ffffffff80a046dc>] setup_arch+0xdc/0x584
+[<ffffffff80a009b8>] start_kernel+0x98/0x940
+Code: 0000 8793 00e7 8305 97ba 8782 b023 00b2 b423 00b2 (b823) 00b2
+---[ end trace 0000000000000000 ]---
+Kernel panic - not syncing: Fatal exception in interrupt
+---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---

Reverting the commit fixes the issue.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds